The present invention relates generally to drilling, boring and milling tools and, more particularly, to a two-edge boring tool and method for boring two concentric holes of precision diameters and precision depths in a single operation.
In the past when boring two concentric holes of different depths and diameters, it has been customary to use two boring machines each having a tool of a different diameter or a single boring machine using first a tool of one diameter, then a tool of another. The disadvantages associated with separate tools, multiple set-ups and special boring machines can be easily appreciated. These include but are not limited to additional capital outlay for equipment, increased down time for tool replacement, problems with maintaining concentricity under strict tolerances and longer product production time adversely affecting overall productivity efficiency.
In order to overcome these problems, special combination cutting tools have been developed for cutting two or more concentric holes in a single operation. An example of such a tool is showing U.S. Pat. No. 4,411,563 to Moon. In its simplest form, the Moon cutting tool includes two sets of cutting edges of different diameters. Both sets of cutting edges are arranged for rotation around the tool centerline to cut two concentric holes of different diameters and depths.
While the Moon cutting tool effectively reduces work handling and eliminates separate machines and operations in boring two concentric holes, it is not without its disadvantages. Since the tool is made for rotation about its centerline, it does not permit any adjustment in hole size. As a result, the tool must be carefully and exactly machined at great production expense. The tools are very difficult to grind or sharpen as each cutting edge set diameter must be precisely to size if a hole of precise diameter is to be achieved. Therefore cutting tools of this type are typically replaced at great expense rather than resharpened. Further, due to machining limitations, it should be appreciated that tools of this type are not suitable when tolerance requirements for the product work piece are held extremely close (i.e under 0.001").
A need is therefore identified for an improved cutting tool capable of boring two concentric holes each of precision depth and precision diameter.